<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html,
        body {
            height: 100%;
            margin: 0;
        }

        .info {
            position: absolute;
            z-index: 99;
            height: 100%;
            overflow: auto;
        }

        .alert {
            white-space: pre-wrap;
            color: #fff;
        }

        canvas {
            position: absolute;
            top: 0;
            left: 0;
        }
    </style>
</head>

<body>
    <div class="info">
        <button id="btn1">test</button>
        <button id="clear1">clear</button>
        <br />
        <div id="alert1" class="alert"></div>
    </div>
    <script src="index.js" type="module"></script>
</body>

</html>